The present invention relates to a transmission unit for automotive vehicles, and more particularly to an improvement of a lubrication device for a differential gear unit of the transmission unit.
In U.S. Pat. No. 4,261,219 issued on Apr. 14, 1981, there has been proposed a transmission unit which comprises a casing arranged to store an amount of lubricating oil in a bottom portion thereof and having a pair of carrier portions at the opposite sides thereof, a differential gear unit arranged within the casing and having a pair of side-journals rotatably supported by a pair of axially spaced side-bearings carried on the respective carrier portions of the casing, a ring gear integral with the differential gear unit and in mesh with a drive pinion on an output shaft of the transmission unit to drive the differential gear unit, a pair of wheel axles extending outwardly through the respective side-journals from side gears of the differential gear unit in an opposite direction and surrounded by a pair of annular seal members carried on the respective carrier portions, a pair of annular shim plates interposed between each of the carrier portions and each of the side-bearings to position the respective side-journals in place, and passages means for leading lubricating oil picked up by the ring gear into a pair of annular side-spaces formed around each of the wheel axles between the respective side-bearings and the respective seal members. In such a construction of the differential gear unit, it is intended to effectively distribute lubricating oil picked up by the ring gear to lubricate the respective side-bearings and the respective side-journals and to lubricate the respective sealed portions of the wheel axles. It has been, however, experienced that sufficient lubrication of the side-journals may not be effected because the lubricating oil from the passage means flows along each peripheral portion of the shim plates and is stored in each oil well formed within each lower portion of the annular side-spaces. For this reason, there will occur unexpected defacement of the side-journals of the differential gear unit, particualry when the vehicle is turning at a high speed.